Al GC velocity ceiling.

[Von Gruff]

There was a thread a while back where the velocity ceiling of the Al GC seemed to be about 1900fps and I can get my AL GC boolits up to here with more than exceptable accuracy. Cu seems to have no such similar ceiling and velocities of 25 - 2700fps have been written about.

The CU GC is usually a comercial one like the Hornady as the GC making tools we have are generally more suited to the .014 that most seem to favour where the Hornadies are in the .018 + range. I have, because of the GC shank dia and the sizing preference of my rifle used a two ply AL GC to get what I need.

CU is not nearly as available in the shim sizes we might use ( and at a suficient thickness is hard enough, even with annealing to be difficult to cut in our GC makers) and the thought crossed my mind that a two ply with a CU outside an AL inner may allow a home made GC to take me to the 2400fps velocity that I have for my hunting loads that are usually GC with the Hornadies because I couldn"t get a AL GC to stay accurate .

So has anybody tried the two ply with differing material and had results that are up to the comercial GC for velocity and accuracy.

I expect there will be those who have had barrel twist and other unique data that may have allowed the AL GC to go past what most of us can get but for the majority of us with standard faster twist barrels origionally designed for j-words the ceiling requires a change to CU.

Von Gruff.

[JeffinNZ]

Hi Gruff.

I am not so sure Al. checks are limited by velocity so much as pressure. For example, my .303 Pygmy will not shoot accurately with a Al. checked bullet at 1800fps with a full load. My SMLE will shoot VERY well with a Al. checked bullet of the same weight at 1900fps. The difference is the pressure.

[Von Gruff]

Jeff, I have the 160gn 7mm boolit that I have been doing most of my trial work with. I guess I should have linked the pressure and velocity but I have tried with Blue Dot, the old ADI 2206 - 3031, and ADI 2209 - H4350 and 1900 or there abouts seems to be where things level out. Different pressure delivery curve going from medium fast to slower didn't make a lot of difference and couldn't get to 2400fps with the AL GC, so wondered about the two alloy two ply GC to get to not having to buy the Hornady GC for my faster loads.

Von Gruff.

[edsmith]

Von Gruff, making a 2 ply check with cu and alu. is a very good idea, some don't like alu. checks, and I am sure a much thinner strip of cu would make it a lot cheaper to make a check the copper guys would like. it bears some looking into. like how thin can the cu be. ect. good idea. Ed. lets keep those ideas comming folks.

[JeffinNZ]

Gruff, I will try some fast loads out over the Christmas break and report.

[caseyboy]

I have used a 22lr casing to punch out a brass check. The bras is about .008" thick. Laminate that with a beer can, and that should get you to .013". I admit that cutting a flattening a 22lr brass is a pain, but for 50 hunting rounds, it is not to onerous.

caseyboy

[Von Gruff]

That might be worth a try caseyboy for a few test boolits.

I have contacted one of the city engineering supply outlets and he says they have access to annealed brass shim that is .010 and they can order it in, but it is about 1/2 meter wide and sold by the meter so will see. I am in the city at the end of the week so will check out pricing and a couple of other outlets then.


Edit to add.
Caseyboy I just went and tried your suguestion and made a very nice wee GC. Used a pair of needlenose pliers and ground the head off a 22 LR case with the linisher then split the side with a pair of heavy scissors. Flatened and punched out the disc, then punched out one from my.012 Al litho plate and formed a two ply brass outer, Al inner GC. Bit labour intensive but in a pinch would be an alternative to sheet stock.

Von Gruff.

[caseyboy]

I have made a couple dozen of just straight 22lr casing checks. At .008" they looked like bottle caps, and seemed to work well enough. I have happened upon some .011" aluminum flashing and that is what I have been using lately. Quick and easy, and I am happy with 1800fps with a 170 30cal boolit. Heck, the deer in my avatar was shot with a 32 win spec unchecked boolit at 1300fps. The boolit went in one side and out the other and breaking the far shoulder joint in the process.